Trim down cselib memory usage

[Geoff Keating]

Jan Hubicka <jh@suse.cz> writes:

> Hi,
> as pointed out in other mail, cselib is responsible for 40% GGC memory
> consumption while compiling conbine.c.
> The datastructures are bnetter to go into allocpool that is whole a lot more
> effecient for such kind of data.  Still it would be worthwhile to look on why
> there are so many containers needed at first place.
> 
> This seems to be responsible for 2% speedup of GCC component test.
> and it also shows the real need for statistics on varpool :)
> 
> OK for mainline/branch?

No, it will cause GC to crash because GCed objects must be allocated
with ggc_alloc.

-- 
- Geoffrey Keating <geoffk@geoffk.org>